I just got my m16 approved and in hand. I tried shooting my 22lr cmmg upper on it (that works in other not FA lowers).

At first it wouldn't even reset the trigger in semi mode. Taking off the BCG weight fixed this and semi auto works.  Then it wouldn't trip the FA sear. Bending the FA trip on the BCG fixed this (but seems like not a great solution).

Now I am at the trigger being reset, FA trip seems to get tripped, next round gets loaded, but no FA firing happens and I have to cycle the BCG to fire again.

I couldn't tell if the issue was too light of a strike on the followup or if wheb the auto sear resets , the slowing down of the BCG from striking it doesn't actually reset the trigger? Not sure.

Any advice on next things to try?

The CMMG and Spike's Tactical forums both have , in their respective pinned sections, troubleshooting information.
Similar information can also be found here:
http://bazookabrothers.com/pages/technical+assistance/3

My personal experience has been that the CMMG ABW is, at about 3/4ths an ounce, on the light side (and has unmitigated bolt bounce) for some configuration/ammo combinations.  Likewise, with an ABW over about 1.3 ounce, some (different) configuration/ammo combinations can be unreliable.  For those reasons, plus the, in my mind, outrageous cost of commercial ABWs, I have made my own DIY 1 ounce ABWs that work reliably and only cost $0.80 each.

FWIW, with one of the DIY one ounce ABWs, in an M16 with standard FCG, a CMMG 9 in. bbl. dedicated upper using CCI MiniMag, 40 gr. ammo for 11 test runs (most done on different days) the rate of fire averaged 1166 rounds per minute with a standard deviation of about 50.

Disclaimer:  I have no affiliation with or financial interest in any vendor or manufacturer.  I am not a competitive shooter or a blogger who receives any form of compensation for endorsements or favorable public or private comments.  I do not have a website.  Use of vendor and/or product brand names, if any, is for informational purposes only; and products or services were purchased by me from regular commercial sources.

Best of luck.
MHO, YMMV, etc.  Be well.

Thank you for the info.

I dont think I'm suffering from bolt bounce as it seems like there is actually not ENOUGH energy to do everything versus too much energy. As I mentioned, I had to remove the weight just to get the trigger to reset and semi to work.

I was thinking maybe I need to try using a lighter buffer spring?

You're welcome.

As for the recoil spring force, there are some suggestions (maybe in the Spike's Tactical guide) that clipping a recoil spring coil or two at a time may help.  It never worked for me.  And FWIW, I also am of the opinion that the Spike's Tactical ABW, at about 0.8 oz., was too light for reliable operation which led them to include the notches, spring, and ball for installing the so-called "ball detent mod" (discussed in the Bazooka Bros. ref previously linked).

If you do not have an anti-bounce weight (of proper mass) and/or the ball-detent mod in place, you will experience bolt bounce.  That ends up with the hammer being in the wrong arc position when falling forward.  In my experience, sometimes there are short burst runs, sometimes only doubling, sometimes there's one round fired and evidence of a light strike on the chambered second round.

Good luck.

MHO, YMMV, etc.  Be well.

ETA: When Max Atchisson designed the M16 .22 conversion about 40 years ago, he had all kinds of resources available to optimize the system.  He came up with the one ounce ABW (now sold by J.A. Ciener, and that I copy as DIY - the patent expired years ago).  My paltry testing has only confirmed that Max was right.  The CMMG ABW is more tolerant of conversion manufacturing tolerances and is easier to install and remove than a Atchisson/Ciener ABW, and works for many, if not most, configuration/ammo combinations.
ETA: Also, the CMMG ABW provides a patented forward assist capability that other ABWs do not have.

I am not sure what length barrel is in the CMMG upper but I had similar issues with my CMMG dedicated upper 9 " barrel upper.

I had trigger reset issues, sear timing issues,  and bolt bounce issues.

To resolve the sear timing issues, instead of bending/tweaking the OEM trip I use one of these sear trips where the timing is adjustable.

https://borebuddy.com/product/adjustable-trip-kit/

To deal with bolt bounce, I got one of these anti-bounce weight systems.  Ended up using two steel and two tungsten weights to finally get the bolt bounce under control.

https://borebuddy.com/product/22lr-bolt-weight/

However with the extra anti-bounce weight mass I then had issues with the trigger resetting in semi-auto as well as some FTEs unsuppressed  (Gun would run well suppressed with the additional backpressure the can provided)

I ended up replacing my disconnector spring with one of these reduced power disco springs.

https://www.gunsprings.com/index.php?page=items&cID=2&mID=1&dID=79#979

I still had some ejection reliability issues even after swapping the disco spring so got these recoil springs and this plug to keep my bolt carrier group from moving around inside the upper robbing energy from the recoil stroke.

https://borebuddy.com/product/22lr-plug/

https://borebuddy.com/product/ar22-rskit/(and run the light 3lbs recoil spring)

With all these changes my kit is finally reliable.  I have only had it out with these mods for a couple of range sessions and probably have 500 to 1000rds though it so long term reliability is still a bit up in the air but I have another friend with a very similar set of mods/parts and his upper runs well.

Unfortunately the extra parts are a couple hundred bucks to its not a cheap option but after owning a couple of these Atchisson style kits over the years this is the first combination I have found that will run with any measure of reliability in full auto.

Hope this helps

In this case, the need to adjust the sear trip timing might be indicative of fore-aft anomaly between the lower and the upper receiver/barrel/.22 unit assembly.  On checking my 4.5 in. and 9 in. bbl. dedicated uppers and a .22 conversion unit installed in a 5.56 barrel, all have the back plate of the .22 unit seated substantially flush with the vertical part of the rear of the upper receiver.  And with the sear trip slid all of the way to the rear of the notches in the .22 unit frame, the distance between the front of the trip tang that engages the auto sear in the lower and the rear of the .22 assembly back plate is 1.5 +/- 0.1 in.

Changing the sear trip timing by changing the sear trip will also alter the reaction timing for the anti-bounce to be effective.  An ABW works by hitting the rear of the bolt at a proper time and with a proper force to cancel the bolt bounce.  Parameters such as ABW weight, ABW rear notch length, sear trip timing, hammer spring force, ammo, and the like are all interactive, but are operable within ranges.

Too much reciprocating mass can slow the bolt down too much such that on firing, insufficient bolt speed can result in failure to extract/eject properly; and on the return stroke insufficient bolt momentum and speed can cause FCG cycling and timing issues as well as failure to properly strip and feed ammo.

Best of luck.
MHO, YMMV, etc.

OK guys, so I have an interesting update.

I got my first set of CMMG auto sear trip and weight kit on the used market because everything was out of stock at the time (it was a never used kit). This is the one I did my testing with that led to the thread.

At the same time I placed a backorder on another CMMG kit because people say it is a good idea to have a backup. Well this one came and it was BLACK instead of CHROME like the first one. It also looks like it was changed a little bit. Did you guys know they have newer version of the same kit?

I tested this one out and everything finally works with no further mods! I didn't even have to bend the sear trip or anything like in the last one. My standard velocity Aguila ammo which is subsonic out of my 9" works in semi but only runs full auto at a maximum 2 rounds. This is solved by using high velocity ammo like golden bullets or Federal Automatch. Out of 40 or so rounds, the Auto Match only FTF 2 rounds. Everything still loaded right but just no ignition. If it's a bolt bounce issue it may be fixed with an adjustable weight and if it is a sear timing issue it may be fixed with the adjustable sear, right?

Either way, I'm mostly satisfied with how it is. Having FTF arent great, but considering it's just a fun gun to plink around with I don't mind that much.

I will be buying the adjustable sear trip kit and adjustable weight set from bore buddy when they come back in stock. Just to see if I could get it working with no FTF or even better if I can get the subsonic stuff working.

OK, I checked the video's and they aren't the best quality after being slowed down and zoomed in. However it doesn't SEEM like it's a bolt bounce issue.

Here is the first video. It fired the first round, loaded the 2nd round but never fired it. Again, it's not great quality, but I don't see any perceptible bolt bounce.



Here is an even worse quality video, and I'm not sure if we could gain anything from it, but from what it's worth it doesn't seem like there is any perceptable bolt bounce either:



Here is a better quality version, but also a flawless run. I don't see anything wrong going on?



Let me know if these videos are way too poor of quality to make anything out. I think I need to get creative to make it better quality (have a tripod hold it really close).

So if there is no bolt bounce, is it likely a sear timing issue that could be resolved with an adjustable sear trip?

Hush now - you're making me want to break mine out and see if I can figure out it's weirdnesses.

As best I can recall, it runs (FA) suppressed, but not bare or with a brake. I want to take the easy way out and blame it on the POS Sporter II RR with that damndable offset bushing up front, but I'll hang on in case I can find other contributors to the problem.

Talking about weirdness on 22lr conversions - i have to flip mine to semi and back to full after every mag change. You can his the sear reset.

Well, just bought the bore buddy adjustable sear trip and AR22 stimulus bundle (which includes a bunch of additions like the adjustable weight, springs, plugs, etc). Hope it wasn't a waste of $300 haha.

When I first got the whole CMMG system it ran like a top.
Weight, rubber plug in front of M16 buffer and the weight. Make sure the weight goes in the right place as its easy to screw up. Ask me how I know.
Last time I was at the range had feeding problems.
Turns out the drum mag wasnt feeding rounds properly with the front of the bullet diving downwards.
Cleaned the mag and problem went away.
The mags get pretty dirty.

Well it turns out I haven't needed to try and use the borebuddy kit yet. The new CMMG kit is working flawlessly. I ran through four 50rd drums with absolutely no hiccups! I was amazed how much fun it is compared to 20 round magazines of more expensive rounds haha. By far my favorite of all the calibers to shoot through my m16 so far.

geezus.   and THIS is why ill be keeping my two Ciener kits and those ugly ass mags forever.  yes, ive replaced several firing pins, extractors and recoil springs over the y... decades but with HV copper plated mini-mags, stingers or winchesters... she runs all day.
FWIW: sear trip timing.  1/10" or less before full bolt lock.  3/32" is the sweet spot.